The invention relates to a monitoring apparatus, as well as to a monitoring method for monitoring a state of wear of a component of a reciprocating piston internal combustion engine in accordance with the description herein.
Large diesel engines are frequently used as drive aggregates for ships or also in stationary operation, for example, for the drive of large generators for the generation of electrical energy. In this respect the motors run as a rule over considerable time periods in continuous mode of operation which represents high demands on the operational safety and the availability. For this reason, in particular long maintenance intervals, low wear and an economic handling of fuel and operation media are central criteria for the operators for the operation of the machines. Amongst other things the piston running behavior of such large bore slow running diesel engines is a decisive factor for the length of the maintenance intervals, the availability and via the lubricant consumption also directly for the operational costs and thereby for the profitability.
Thereby an always greater significance is given to the complex problem of the lubrication of large diesel engines.
In large diesel engines, however, not only for these, the piston lubrication occurs via lubrication devices present in the piston moving to and fro or within the cylinder wall, by means of which lubrication oil is applied to the running surface of the cylinder wall to minimize the friction between the piston and the running surface and therefore to minimize the wear of the running surface and the piston rings. For example, the wear of the running surface currently lies at less than 0.05 mm for an operational time of a 1000 hours for modern machines such as e.g. the RTA motors of Wärtsilä. The quantity of lubricant conveyed for such engines lies at approximately 1.3 g/kHh and less and at least for reasons of cost should still be reduced as far as possible, wherein the wear should be minimized at the same time.
Very different solutions are known as lubrication systems for lubricating the running surfaces, both with regard to the specific design of the lubrication device itself and also with regard to the method of lubrication. For example, lubrication devices are known in which the lubrication oil is applied through a plurality of lubricant openings onto a piston running past the lubricant openings which are arranged in the circumferential direction in the cylinder wall, wherein the lubricant is distributed through the piston rings both in the circumferential direction and also in the axial direction. In this method, the lubricant is not applied on a large scale onto the running surface of the cylinder wall, but more or less point-wise between the piston rings on the side surfaces of the piston.
Independent of which method is used to apply the lubrication oil onto the counter running partner, specific problems in connection with the cylinder lubrication and, in particular in connection with the wear of the components of cross-headed large diesel engines exist which up until today have remained unresolved.
In this respect it is known to at least coarsely determine the state of wear of pistons, piston rings, gas exchange valves, such as e.g. the outlet valve, the running surface and other components of the internal combustion in that specific properties of the lubrication oil used in the internal combustion engine are investigated. For this purpose the lubrication oil which, for example, collects at the bottom of the piston bottom side space in the case of longitudinal scavenged two-stroke large diesel engines, is collected in a container and the collected lubrication oil is investigated, for example, on the presence of iron particles. When a certain quantity of iron is then determined in the thereby collected lubrication oil this permits certain crude conclusions on the state of wear of the aforementioned cylinder components. In this respect the measurement of the iron content occurs in a manner known per se by means of a magnetic method.
These known methods, however, have a series of disadvantages which frequently severely distort the measurement results in practice.
For example, the lubrication oil which has settled, for example, at the floor of the piston bottom side space, is contaminated with many other materials which did not originally emerge from the combustion space of the internal combustion engine. For example, contaminants are transported into the receiver space from the turbo charge system which additionally contaminates the lubrication oil. Naturally, a certain quantity of contaminated lubrication oil is also always conveyed from the crankshaft space into the piston bottom side space through the stuffing boxes. Moreover, the lubrication oil stored in the receiver space is always a mixture of contaminated lubrication oil which is composed of very many past engine cycles, so that the lubrication oil settled in the receiver space never represents a current composition of the lubrication oil, as it corresponds to the current real composition of the lubrication oil in the cylinder liner.
This means that the lubrication oil settled in the receiver space includes a whole series of residues which either do not stem from the corresponding cylinder liner and/or do not correspond to the current situation.
A further grave disadvantage of the known measurement methods lies therein that the magnetic measurement systems used have a far too small a sensitivity. This has the effect that a comparatively large quantity of lubrication oil has to be collected. The lubrication oil is typically collected in a container which has a volume of a few 10 cm3 which has to be more or less completely filled before a measurement can actually be carried out. The lubrication oil consumption of, for example, a modern large diesel engine has been strongly minimized as was initially mentioned, so that it typically takes many hours until a sufficient quantity of lubrication oil has been collected, which can then be investigated in the known measurement systems.
The disadvantages are obvious. Real online measurements in the sense that a current state of wear of the engine components can be determined are not at all possible, as a measurable sample of lubrication oil has to be collected over a long period. This has the effect that, for example, a starting seizure of the piston at the cylinder running surface, i.e. the feared scuffing, is frequently only noticeable too late. Frequently only so late that massive damage at the cylinder components can no longer be avoided. The result is that a cylinder liner has to frequently be taken out of operation and be replaced.